The present invention is directed to a method for establishing a protected communication segment between two network elements of a telecommunication network as well as to a corresponding telecommunication network.
FIG. 1 shows such a protected segment of a telecommunication network, this comprising a protected connection PECT (standing for xe2x80x9cProtectedxe2x80x9d) and a connection PING (standing for xe2x80x9cProtectingxe2x80x9d) that protects this connection. Given the example shown in FIG. 1, the protected connection PECT proceeds from a network element NEa via network elements NEb and NEc to a network element NEz. Via intervening network elements NEd and NEe, the protecting connection proceeds parallel to the protected connection PECT, i.e. likewise proceeds between the network elements NEa and NEz. As shall be explained in greater detail below, the switching or establishment of the protected connection PECT and of the protecting connection PING is initiated by a management system MS of the telecommunication network.
The individual network element NEa . . . NEz are connected via corresponding termination points to a neighboring network element, whereby the termination points belonging to one and the same connection are connected via what is referred to as a cross connection. Given the example shown in FIG. 1, the two network elements NEa and NEz between which the two connections PECT and PING proceed therefore comprises termination points TPa . . . TPc, whereby a cross connection cCC that contributes to the protected connection PECT and therefore conducts the communication traffic must be respectively established between the two termination points TPa and TPb of the network elements NEa and NEz, whereas a protecting cross connection pCC contributing to the protecting connection PING must be respectively established between the two termination points TPa and TPc of the network elements NEa and NEz.
The management system assigns an attribute to every individual cross connection, this attribute unambiguously characterizing its function. For example, this attribute can assume the values xe2x80x9cconnectedxe2x80x9d, xe2x80x9cprotectingxe2x80x9d and xe2x80x9cnot connectedxe2x80x9d. When a cross connection has the attribute xe2x80x9cconnectedxe2x80x9d, this means that this cross connection conducts the actual communication traffic. These cross connections are referenced below as xe2x80x9ccCCxe2x80x9d (standing for xe2x80x9cconnected cross connectionxe2x80x9d) and are shown in FIG. 1 in the form of solid double lines within the individual network elements NEa . . . NEz. When a cross connection has the attribute xe2x80x9cprotectingxe2x80x9d, this means that this cross connection has a protecting function for another cross connection with which it shares exactly one termination point and that has the attribute xe2x80x9cconnectedxe2x80x9d. Cross connections are referenced xe2x80x9cpCCxe2x80x9d below (standing for xe2x80x9cprotecting cross connectionxe2x80x9d) and are shown in FIG. 1 in the form of broken double lines. A cross connection that has the attribute xe2x80x9cnot connectedxe2x80x9d is treated like a cross connection that does not exist. This attribute only plays a part for the sequence of the generation of the protecting pCC cross connections since it is always assumed for the generation of a pCC cross connection that the corresponding cross connection previously had the attribute xe2x80x9cnot connectedxe2x80x9d.
Protecting pCC cross connections are only present in those network elements NEa and NEz in which a protected connection and a corresponding protecting connection branch. A network element in which both the cCC cross connection of the protected connection as well as the pCC cross connection of the protecting connection lie automatically switch the communication traffic from the cCC cross connection onto the pCC cross connection if an interruption of the traffic on the protected connection occurs.
It proceeds from the above description that the establishment and switching of the cCC cross connections and pCC cross connections is of critical significance for the activation of the protected segment or, respectively, of the protected connection PECT and of the protecting connection PING. What is thereby understood by an activation of a connection is the physical establishment of the connection, so that the two termination points of the corresponding connection are physically connected to one another after a successful activation, whereby two termination points within a corresponding network element are physically connected to one another upon establishment or creation of a cross connection.
At the time the protected segment is activated, however, cross connections can already be present in the two network elements NEa and NEz, these having been previously locally switched by the operator of the telecommunication network or having not been eliminated after a circuit because of a system error. In the former instance, communication information can already be transmitted via these already existing cross connections at the point in time of the activation of the protected segment, so that these cross connections already existing before the activation of the protected segment dare not be eliminated or deleted. On the other hand, there is the need to activate the protected segment as requested, i.e. to have the protected connection PECT proceed via the network elements NEa-NEb-NEc-NEz and the protecting connection PING proceed via the network elements NEa-NEd-NEe-NEz in the example shown in FIG. 1.
This problem was hitherto solved such that, before activation of a protected segment, the management system MS has viewed the constellation of existing, locally switched cross connections in the two terminating network elements NEa and NEz together in order to activate the protected connection PECT and the protecting connection PING. The problems that arise given this procedure shall be explained in greater detail below on the basis of the illustrations of FIG. 3, whereby it must be noted that the management system MS administers the protected segment in the form of a model in which the protected connection PECT and the protecting connection PING are modelled. The model assumes that the termination points TPa and TPb of the two network elements in FIG. 1 are respectively connected by a cCC cross connection, whereas the termination points TPa and TPc must be respectively connected by a pCC cross connection. When, as shall be explained in greater detail later on the basis of FIG. 3, a constellation of the cross connections that cannot be reconciled with this model already exists in the two network elements NEa and NEz before the activation of the protected segment, the constellation cannot be described by the model. The result of nonadherence to the pre-conditions would be that the forward and return direction of the traffic proceeds differently (in this case, the traffic given the arrangement shown in FIG. 1 would proceed, for example, from NEa to NEz via NEd and NEe and from NEz to NEa via NEc and NEb), i.e. the position of the protected connection and the protecting connection is not the same then for the forward and return direction of the traffic but depends on the direction of the traffic. A model that could also describe these cases is in fact fundamentally possible. However, it would be significantly more complicated.
A cCC cross connection, i.e. a cross connection with the attribute xe2x80x9cconnectedxe2x80x9d, cannot be established between two termination points (for example, between the termination points TPa and TPb according to FIG. 1) when one of these two termination points is already connected to another cross connection that has either the attribute xe2x80x9cconnectedxe2x80x9d or the attribute xe2x80x9cprotectingxe2x80x9d. As has already been mentioned, in contrast, it is a pre-condition for the establishment of a pCC cross connection, i.e. a cross connection with the attribute xe2x80x9cprotectingxe2x80x9d, that a cross connection with the attribute xe2x80x9cnot connectedxe2x80x9d is already present between the corresponding termination points. The establishment of a cross connection with the attribute xe2x80x9cnot connectedxe2x80x9d is always possible. However, a cross connection with the attribute xe2x80x9cnot connectedxe2x80x9d can only be turned into a pCC cross connection when one of the two termination points (not both) is already connected to a cCC cross connection (for example, either the termination point TPa or the termination point TPc according to FIG. 1) and this cCC cross connection is not already protected by another pCC cross connection. These previously explained adaptation rules for taking over already existing cCC or pCC cross connections must thus be adhered to in the establishment of the individual cross connections in the network elements NEa and NEz.
The individual illustrations of FIG. 3 show respectively possible constellations for the cross-connections that are already locally switched before an activation of the protected segment between the two network elements NEa and NEz. Let it thereby be assumed that the protected segment shown in FIG. 1 with the protected connection PECT proceeding at the top and the protecting connection PING proceeding at the bottom is to be activated. It is explained below how the previously known management system MS reacted to the constellations shown in FIG. 3.
Given the constellation shown in FIG. 3A, all four cross-connections are already present in the two network elements NEa and NEz, whereby these cross-connections, however, respectively have the incorrect attribute value, i.e. a protecting pCC cross-connection respectively proceeds between the termination points TPa and TPb, whereas a cCC cross-connection is present between the termination points TPa and TPc. This results in the protected connection in the telecommunication network proceeding at the bottom and the protecting connection proceeding at the top. Thus, the position of the protected connection PECT and the position of the protecting connection PING have been interchanged with one another. This special case was already capable of being handled by the previously known management system MS in that the model was correspondingly adapted before the activation of the protected segment. Subsequently, the protected segment was capable of being successfully activated.
Given the constellation shown in FIG. 3B and taking the above-explained adaptation rules into consideration, the requested cCC cross-connection cannot be established between the termination points TPa and TPb of the network element NEa since the termination point TPa is already connected to a cCC cross-connection (leading to TPc). The same is also true of the constellation shown in FIG. 3C, whereby the desired cCC cross-connection between the termination points TPa and TPb cannot be established in the network element NEc either for the same reason.
Given the constellation shown in FIG. 3D, the cCC cross-connection carrying the traffic cannot be established in the network element NEa between TPa and TPb as desired, since the termination point TPa is already connected to two cross-connections, namely a cCC cross-connection between TPa and TPc and a protecting pCC cross-connection between TPa and TPb. Although a cross-connection is thus already present between the termination points TPa and TPb, this has the incorrect attribute xe2x80x9cprotectingxe2x80x9d.
Given the constellation shown in FIG. 3E, all four cross-connections are in fact already present, whereby, however, the cross-connections present in the network element NEa respectively have the incorrect attribute. Analogous to FIG. 3D, an establishment of the cCC cross-connection between TPa and TPb of the network element NEa is therefore not possible.
Given the constellation shown in FIG. 3F, finally the desired cCC cross-connection between the termination points TPa and TPb is in fact already present, so that the as yet lacking, protecting pCC cross-connection between the terminal points TPa and TPc could be established. In the network element NEz, however, the cCC cross-connection between the termination points TPa and TPb cannot be established, analogous to the cases shown in FIGS. 3D and 3E, since a pCC cross-connection is already present, i.e. a cross-connection having the incorrect attribute value xe2x80x9cprotectingxe2x80x9d.
As has already been briefly mentioned, the constellation of the cross-connections that are already locally switched in the network elements NEa and NEz were viewed together in order to determine the position of the protected connection PECT and of the protecting connection PING. When all four cross-connections with the respectively incorrect attribute were already present in both network elements NEa and NEz (see FIG. 3A), the roles of the protected connection and of the protecting connection were interchanged in the model of the management system MS in order to adapt the model to reality. Subsequently, the activation of the protected segment was implemented with the position of the protected connection and the protecting connection interchanged compared to the original intent.
The constellations shown in FIGS. 3B through 3F, however, were not capable of being previously adapted or activated. In particular, the cross-connections in the network elements NEb . . . NEe were also not switched in these cases. Instead, the compulsory cancellation or elimination of the cross-connections already existing and locally switched was required in these cases in order to be able to establish the protected segment as desired. This, however, in turn resulted in the traffic already proceeding via the locally switched cross-connections was temporarily interrupted.
An object of the invention is to provide a method for establishing a protected communication segment between two network elements of a telecommunication network as well as a corresponding telecommunication network, whereby an improved adaptation, i.e. take-over of already existing cross-connections is enabled given the activation of the communication segment.
In a method and system of the invention for establishing a protected communication segment between two network elements of a telecommunication network, the protected communication segment between a first network element and a second network element is provided as a protected connection and a protecting connection. The first and second network element are provided as respective termination points via which the respective network element is connected to a neighboring network element. A first cross-connection carrying the communication traffic between a first termination point and a second termination point for the protected connection and a second cross-connection between the first termination point and a third termination point protecting the corresponding first cross-connection for the protecting connection are respectively established within the first and second network elements of the protected communication segment. The first and second cross-connections in the respective or second network elements are established independently of cross-connections already existing in the respective second or first network element.
In contrast to the previously procedure, the two network elements between which the protected segment is to be established and activated are not inventively viewed in common but independently of one another. As a result thereof, the plurality of constellations to be considered is reduced from the previous N2 to N. Due to this reduction, the complete handling of all possible constellations of already existing cross-connections in these two network elements is possible with a justifiable cost-to-benefit ratio. In particular, all adaptable constellations shown in FIG. 2 can also in fact be adapted with this procedure, i.e. taken over. It is only in a following step that the attributes of the cross-connections already existing are checked. If a constellation had been adapted that cannot be described with the existing model, a corresponding alarm is preferably output to the operator of the telecommunication network.
The special quality of the inventive solution is thus comprised, on the one hand that the two sides of a protected segment are viewed independently of one another in view of the already existing cross-connections and, on other hand that already existing or locally switched cross-connections are fundamentally adapted when the corresponding constellation cannot be described with the existing model, i.e. even given the presence of constellations that cannot be described with the model, the corresponding connections are switched, so that the traffic can run in any case. As a result of the output of an alarm to the network operator provided in these cases that cannot be described with the model, it is assured that the network operator can then take appropriate measures.
The invention is explained in greater detail below on the basis of a preferred exemplary embodiment with reference to the attached drawing.